The present invention relates to a light emitting diode, especially to a light emitting diode that increases illumination efficiency of light source.
Light emitting diode (LED) is a fine solid-state light source made of semiconductor material. The light source includes two electrodes. After being applied with voltage (minimum current), the electron-hole recombination process produces some photons due to energy gap of electrons and electron-holes when electrons cross the junction from the n- to the p-type material. The LED is different from a general light bulb and it features on low power consumption, with long lifetime, low driving voltage, and fast reaction. Moreover, the LED has compact volume, and good shock resistance so that it's suitable for mass production in the form of mini or array-type elements. It has been applied to electrical appliances, computers and communication products and has become one of the essentials in our daily lives.
According to wavelength, LED is divided into visible LED (wavelength from 450 to 680 nm) and invisible LED (wavelength from 850 to 1550 nm).
Once being classified by material of the epitaxy layer, the LED is divided into four categories: binary compound (such as GaAsGaSbGaN etc.), ternary compound (such as AlxGal-xAsAlxGal-xPInl-xGaxAs etc.), quaternary compound (such as AlInGaPInAlGaAsAlxGal-xAsyPl-y etc.) and GaN-based compound.
If being differentiated by the brightness, there are two types-high brightness LED and the general LED. However, the light from LED is directive and each manufacturer has different standard for illumination. It's difficult to differentiate the high brightness LED and the general LED correctly. Moreover, the brightness and the illumination efficiency of the LED are related to material of the epitaxy layer. It's preferred to use material of the epitaxy layer as criterion to define and brightness. The high brightness LED is formed by quaternary compound and GaN-based compound while the general LED is made from binary compound/ternary compound except GaN-based compound.
Since 1968 a first commercial LED is developed by HP (Hewlett-Packard), functions and applications of the LED are improved dramatically along with improvement of material and manufacturing processes. According to Haitz's law, brightness of the LED is doubled per 18˜24 months while the cost of each unit is reduced to about one tenth per one decade. In recent years, applications of the high brightness LED are getting broader. Besides outdoor displays and traffic signs, the high brightness LED is also used in light sources of vehicles and backlight sources of LCD on portable electric appliances. After analyzing global market of high brightness LED in 2003, the main application is in portable electric appliances, especially the camera phones. Due to population of mobile phones with colorful displays and camera phones with flashlight, demands for high cost white-light LED increase dramatically so that the mobile phones achieves about 41% market share of the high brightness LED in 2003. Compared with the amount in 2002, the market share grows 3%. As to the LED for the future, due to increasing improvement of illumination efficiency and brightness of LED, Mercury became one of the forbidden materials to be used in EU after 2006, and increasing cost of global energy, it is expected that high brightness LED is going to replace other light sources available now in the market of illumination devices, vehicles and middle/large size displays. Generally, high brightness LED is still a niche product in illumination products. Just like clothes and food, the amount of illumination devices should be satisfied firstly and then the quality is required. Without sufficient light or brightness, individual's working efficiency or vision may be affected. This also has negative effects on people's physical and mental health.